The present invention relates generally to the field of fluid displacement apparatus, and more particularly, is directed to improvements in scroll type fluid compressors.
Scroll type fluid displacements apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 issued to Creux discloses such a device which includes two scrolls each having a circular end plate and a spiroidal or involute spiral element. The scrolls are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scrolls shifts the line contacts along the spiral curved surfaces and, as a result, the volume of the fluid pockets changes. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, a scroll type fluid displacement apparatus may be used to compress, expand or pump fluids.
An orbiting scroll element 1 and a fixed scroll element 2 are shown interfitted in FIG. 1. Because the scroll elements are angularly and radially offset, fluid pockets 3 are formed between respective side walls of the scroll elements. As scroll element 1 is orbited about fixed scroll element 2 with a radius 0--0'; the volume of fluid pockets 3 is gradually decreased. FIG. 1(b) illustrates the size of fluid pockets 3 after the scroll elements have been rotated 90 degrees from the position shown in FIG. 1(a). FIGS. 1(c) and 1(d) show the corresponding size of fluid pockets 3 after orbiting scroll element 1 has been rotated 180.degree. and 270.degree., respectively. By the time orbiting scroll element 1 has been rotated 360.degree., fluid pockets 3 have merged at their respective center 0 and 0' as shown in FIG. 1(a). Also by this time, a new set of fluid pockets 3 have formed and taken in fluid for compression during the next orbit of orbiting scroll 1. Compressed fluid at the center of the interfitted scroll elements is discharged through a port as indicated by reference No. 5 in FIG. 1(c).
In a scroll type compressor as described above, fluid is compressed by reducing the volume of the fluid pockets as the orbiting scroll rotates about the fixed scroll. The fluid pockets are formed by the curved surfaces of each element coming into contact. If the scroll elements are precisely constructed, sufficient line contacts can be formed to seal the fluid pockets by using a bushing as disclosed in Japanese Patent Publication No. 58-19875. The seal which is formed between the axial end surface of one scroll element and the surface of the end plate of the other scroll element is achieved by grooves which are formed on the end surface of each of the scroll elements. Seal members are disposed in the grooves to seal the scroll elements. The grooves are usually formed so that their center line corresponds to the center line of the scroll elements so that the groove at the center portion of the scroll elements correspond to the involute of the scroll element.
During operation of the scrolls to compress fluid, the pressure along the outer wall of the above mentioned groove is greatly increased. This pressure F can be expressed by the equation F=(P1-P2).times.L1.times.L2 where:
P1=the pressure at the center portion of scroll elements.
P2=the pressure at the intermediate chamber of the scroll elements.
L1=is the height of the groove.
L2=is the length of the groove.
The exertion of such a force along the walls of the grooves, particularly the outside walls, leads to premature deterioration of the grooves and ultimate destruction of the scroll elements.
Moreover, because the seal element within the groove is in tight contact against the end plate of the opposite scroll element and moves slightly with it in response to the relative movement of the scroll elements, there is additional frictional contact force exerted on the inside and outside walls of the groove during the orbital motion of the orbiting scroll element. Thus, the outside wall of the groove along one half of each scroll element is pushed toward the outside and the inside wall of the groove along the other half of the scroll element is pushed toward the inside. The direction of the force against the outside and inside walls of the groove continuously changes due to the relative orbital motion of the scroll elements. Since the outside wall of the groove thus receives the above mentioned fluid pressure F and the frictional contact force, the outside wall is especially susceptible to deterioration.